Bad master (brake cylinder)?

[2003SV]

Not sure where this topic should go so apologies in advance.

I just tried to bleed the brakes on my Shell Valley Cobra (it uses GM Intermediate discs and has 2 master cylinders, one for the front brakes and one for the rear brakes). I hadn't run the car in about 2 years and one of the master cylinders (for the front) looked to be nearly dry. I added fluid and then tried bleeding with the help of my pit crew (wife).

I can't seem to get air from the front brakes... I bet I filled the master cylinder up 5-6 times. I'd have the pit crew press down as I opened the bleed screw and she'd hold the pedal until I closed the bleed screw. I was careful to ensure the master never ran out of fluid and topped it off, each round of 3 presses. I couldn't seem to get air out completely from the passenger side and so I switch to the driver's side. And it was the same thing. After 3 fills of the master the driver sides still coughs up air and I gave up.

I bought the car used and so it could be this master (Wilwood) is ?18 years old...

I'm guessing this master is bad... would you agree?

Thanks in advance.

[HighPlainsDrifter]

Hi,
if it was dry or low you have a leak, fluid out + air can get in. check your rubber disc brake hoses and copper washers, need new ones.
Perry

[twobjshelbys]

So if you filled it that many times where did the fluid go??? I'd start there...

[2003SV]

Sorry if I wasn't clear. After 3 or 4 bleed presses (open bleed, press brake, close bleed, allow pedal to return to top), I'd top off the master cylinder. I was catching the purged fluid in an oil bottle. I topped off the master in that manner probably 6 times passenger side and then 3 times driver's side and each time pushed fluid and air (I was using clear plastic tubing).

I guess I'll have to get the car up on jack stands again and stomp on the brakes to see if there's a leak as the master shouldn't have been down so low even after 2 years of not running...).

[strictlypersonl]

The caliper bleed screw is at the top? It's possible that the calipers were installed on the wrong sides.
Also, look for high places in the lines to the caliper which might retain air at the top of bends.

[2003SV]

Yes, the bleed valves are at the top of the calipers. They are relatively new. I think I replaced what was there 4-5 years ago. If they are installed incorrectly (wrong sides) think THIS IDIOT (me) did that....

I may yet try one more thing but I've honestly have never see this much fluid/air continue to be pushed out. I probably went through 16 oz of fluid... It makes sense that if the cylinder was nearly out of fluid (and my pads are new), that I have to have a leak somewhere. So I guess first order is to try to find if/where I have a leak.

[strictlypersonl]

Not that it would be a permanent solution, but you might try Pressure Bleeding. If it fixes the problem, it would narrow the focus to the master cylinder.

[Gary Baxter]

replace brake master cyl . probably sucking in air when letting up pedal during bleeding.no other leaks found?

[bobcowan]

Press on the pedal hard. Open the bleeder only 1/4 turn. Close the bleeder. Release the pedal.

If you open the bleeder too much, air can get in around the threads. If you open the bleeder when the system is not under pressure, air will enter.

Use a simple bleeder cup so that even with a little bit of back flow it will only backflow fluid, and not air.

If fluid is coming out the bleeder under pressure, then the MC is working. As long as the ports at the bottom of the reservoir are covered, there's no place for it to suck in air.

If the fluid out is roughly equal to the fluid in, there's not much of a leak.

[2003SV]

I think I only crack the bleed 1/2 turn maybe less as there isn't much room to swing the wrench through a huge arc ... I'm careful to ensure the pedal isn't raised until I close the bleed. I generally haven't had this issue but geez I rarely bleed anything...

I stepped on the brakes last night thinking I'd find a leak somewhere. I stepped pretty darn hard, but it wasn't incredibly hard to the point I was standing on the pedal and the pressure held. I did that 3 or 4 times and the pressure held. My brake routing in the front is pretty easy to see from the engine compartment right to the calipers. Nothing, nada, zero, zilch... so no leaks as far as I could see.

Very mysterious... I'm wondering if fresh fluid and the pumping action has lubricated the rubber piston 'cups'? I'm also wondering if there's space between the passenger compartment and the firewall where if the master was leaking slightly (from the rear) it'd drip into that space???? Anyway, right now I have the brakes I remember, at least the pedal height and 'feel'. It's not brick hard immediately, but there's a bit of a take up and then the pedal firms up. It's about what I remember... So I guess I should just monitor what's going on. I'll check fluid level as it filled it to the upper fill mark. (That said, it's very hot and humid here so I'm not going to work a great deal on the car in the evening..) Thanks much to all for looking over my issue and responding. If it looks like I'm losing any fluid, I'll just replace the master... And that's not TOO bad, as it's the most easily accessed master cylinder. Thanks again!

[ERA 626]

watch this video, then buy a couple purge bottles like in the vidieo on amazon cheap... thank me later...
https://www.youtube.com/watch?v=jELllXdtjdc

[2003SV]

I actually came across that video about a week ago... It's an interesting concept but I think it works only if you gravity feed to point of having all air out of hoses before you press the brake pedal several times. I'll have to check on Amazon and see what those bottles run! Thanks.

[cycleguy55]

Since using quick / speed bleeders I've done nothing else. Great invention.

[incoming]

I built a power bleeder out of a pump up sprayer and can bleed my army deuce by myself in about 45min. That's pushing about a gallon and a quart of fluid. DOT 5 changed colors when moisture gets in it and you just push till you get fresh fluid.